The purpose of this research proposal is to elucidate further the initial means by which catecholamines affect cellular function. This inquiry has become possible through techniques recently developed to measure beta adrenergic receptors directly and to prepare responsive membrane components from target cells. The features of the interaction between beta adrenergic catecholamines and their receptors will be studied with regard to the characteristics of the interaction, the biological consequences, and the membrane-associated factors that control the interrelationship between these two events. Application of this information to selected clinical problems will help to answer heretofore outstanding problems of clinical importance such as the relationship between thyroid hormone and catecholamines and the pharmacokinetics of the bioactive forms of propranolol.